# How are glycosidic linkages formed?

I know a condensation reaction occurs, with the loss of water.

But which OH is lost? The O in the linkage belongs to which monosaccharide?

Example: take sucrose, the O in the linkage belongs to fructose or glucose?

I couldn't find any literature regarding this. Any help is appreciated .

In sucrose molecule the glycosidic linkage is formed by the OH group on the anomeric carbon of α-D-glucose and the OH group on the anomeric carbon of β-D-fructose.

source :

https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%3A_Organic_Chemistry_(McMurry)/Chapter_25%3A_Biomolecules%3A_Carbohydrates/25.08_Disaccharides

As seen, in either alpha d-glucose or beta d-fructo furanose may react to give sucrose.

Let us examin.

Alpha D-gluco Pyranose gives an intermediate 1 and 2 by protonation at anomeric carbon.

Similarly Beta D-fructo furanose gives an intermediate 3 and 4 by protonation at anomeric carbon.

If you examine , structure 3 is more stable then structure 4.

The negative inductive effect of CH2OH in fructofuranose destablizes this intermediate 4.

Hence structure 2 , an intermediate of aplha D-gluco pyranose (more stable) attacks beta D-fructo furanose togive sucrose.

The above diagrams are author drawn in CHEM DRAW

• This entire answer appears to be copy-pasted from Bruice's Organic chemistry. If you are quoting third-party sources, or using any graphics/data/plots that are not made by you, put an appropriate reference and denote the part that is quoted with proper markup (>). Keep in mind that if you don't that you may eventually be accused of plagiarism. – andselisk May 26 '19 at 7:23
• @user226375 your question is answered now, – Chakravarthy Kalyan May 26 '19 at 8:42
• @andselisk you were correect .This was taken from Bruice's Organic chemistry.(missed reference ).How ever the answer is rewritten ti the question asked .The diagrams are mine , drawn on CHEMDRAW. – Chakravarthy Kalyan May 26 '19 at 8:44
• @andselisk I MISSED QUOTING REFERENECE IN HURRY TO ANSWER .MY APOLOGIES .THIS WAS NOT DONE ON PURPOUSE. – Chakravarthy Kalyan May 26 '19 at 8:52